It’s good when developers listen. Back when I tried a preview build of the shooter/tower-defense hybrid Sanctum 2, I had only one significant complaint: At the beginning of each round, the game would throw your new materials on the ground for you to pick up, instead of giving them to you automatically. This seemed like a waste of time.

Lo and behold, resources now appear in your inventory automatically -- and the rest of the game is just as exciting and fresh as it was back when I wrote my preview. So if you like shooters and you like tower defense, I would highly recommend you pick this game up. At $15, it costs about a buck for each amazing half-hour level.

Sanctum 2 is pretty simple, even if you've never played the original. On each of the maps you'll face about ten waves of enemies. Before each wave, you have some time to set up a system of tower defense -- you'll have tower bases, along with various kinds of turrets to put on top. When you're done, the wave begins, and you go into first-person shooter mode, personally blasting any enemies your turrets can't take care of.

The idea, obviously, is to force your enemies through an elaborate maze, giving you and your turrets time to kill everything. Any enemies that make it through will attack your Core, the glowing orb you're trying to protect. If your core runs out of health, it's game over. If you run out of health, by contrast, all you get is a ten-second time-out.

The shooter gameplay here is interesting -- it has a definite Halo influence, with alien weaponry, low-gravity jumping, and a two-weapon-at-a-time limit. Switching weapons is strongly encouraged; somehow, your character manages to reload one weapon while firing another, so if you keep switching you can deal damage pretty much constantly. In addition, you have four different classes to choose from, though they're nothing new -- assault rifle, shotgun, sniper rifle, and flamethrower.

The tower-defense gameplay is a different animal. You have to pick the right turrets for each battle, and then deploy them carefully to maximize the damage they deal to enemies. The level design is a definite highlight here -- you really have to spend some time just walking around to figure out the best way to set up your maze. You also need to make tough calls between creating new turrets and upgrading old ones to make them more powerful.

The enemies are well designed, too. Each has its own personality -- there are little guys who swarm you, flying enemies who soar right above your turrets, huge armored walking monsters, and even bosses who are capable of tearing down your towers. Every time you think you have it figured out, a new creature shows up and makes you change your strategy.

There's an RPG leveling system here as well. With each level you unlock new guns, new turrets, and new perks, adding an extra layer of complexity to the whole experience and making your losses a little less frustrating, because even failure earns you EXP.

I played Sanctum 2 alone for the most part, and I had a blast -- the tower-defense puzzles really lend themselves to solitary play. No one wants to sit around and watch you think. But for those who want to work together, there's online multiplayer for up to four players, and while there were a few major flaws at launch, a patch has already cleared them up.